1. Field of the Invention
This invention relates generally to semiconductor devices and to the fabrication of semiconductor devices, and more specifically, this invention relates to RC-Networks in semiconductor devices and to a fabrication method for semiconductor devices comprising Resistor-Capacitor (RC) networks. Variations of semiconductor devices comprising RC networks include devices such as Resistor-Capacitor-Diode (RCD) networks and Resistor-Capacitor-Inductor (RCL) networks.
2. Description of the Related Art
In the prior art, certain methods of improving the electrical conductivity of capacitor electrodes in semiconductor devices using thin film polysilicon plates have been disclosed. One such approach may be found in Tung et al. (Tung) U.S. Pat. No. 5,682,060 issued on Oct. 28, 1997. Tung discloses a process for fabricating a capacitor component in a semiconductor device which is comprised of a bottom doped polysilicon plate, a dielectric layer, typically oxide or oxide/nitride/oxide (ONO), and a top doped polysilicon plate.
Following the deposition and doping of the top polysilicon plate, a layer of metal silicide, preferably titanium silicide, is formed on the top doped polysilicon plate. The titanium silicide layer is formed when the device is heated to a temperature of 675 deg. C. for a period of 30 minutes after a layer of titanium is deposited on the top doped polysilicon layer. The result is the formation of titanium silicide over the top doped polysilicon plate thereby improving the electrical conductivity of the top plate. The unreacted titanium is removed by a chemical process well known in the art. Fabrication of the remainder of the device including isolation layers and metal contacts may then be completed.
The disadvantages of the above described Tung patented method are the time and cost involved with the thermal or heating process to produce the titanium silicide. There may also be process inconsistencies or incompatibilities with the metal silicide formation approach resulting in electrical anomalies across the numerous devices typically fabricated in a single integrated circuit type of silicon wafer.
Other methods which use tantalum nitride or other types of nitride for a resistive layer have the very severe problem of nitrogen contamination of the capacitor electrodes, the metal contacts to the capacitor electrodes and/or the metal interconnect layer or layers. Nitrogen contamination results, for example, in instability in the capacitive devices.
Therefore, a solution to the above described limitations imposed by nitrogen contamination found in the prior art and by the metal silicide prior art method for fabricating capacitors to be used in an integrated circuit using semiconductor devices was needed, particularly for those semiconductor devices or integrating circuits incorporating RC networks.